1. Field of the Invention
The invention relates to a device for moving and positioning an object in space, having at least three actuating arms that are each connected to a motor/transmission unit and are pivotable around a transmission axis, a support element provided for arranging at least one gripping mechanism for gripping the object; at its free end, each actuating arm has a first articulation axis extending parallel to the transmission axis, with first joint parts spaced apart from each other, each belonging to a respective first ball joint; the support element has a second articulation axis associated with each actuating arm, with first joint parts spaced apart from each other, each belonging to a respective second ball joint; the first articulation axis is connected to the second articulation axis by means of a pair of connecting rods that have second joint parts at the ends and, together with the first joint parts on the first articulation axis and the first joint parts on the second articulation axis, these second joint parts at the ends of the connecting rods form the first and second ball joints; and the connecting rods are connected to each other in order to stabilize the ball joints. The device for moving and positioning an object in space is a device referred to in professional circles as a robot with parallel kinematics.
2. Description of the Prior Art
A device with three parallelogram rod assemblies of the type mentioned at the beginning, which is also referred to as a “delta robot,” is known from WO-A-03/106114. The two connecting rods composed of a stiff material and belonging to a parallelogram rod assembly have pairs of pins that protrude laterally in the region of the bail joints. Pairs of O-rings composed of a rubber-elastic material are elastically stretched into place around the pins on opposite sides of the connecting rods. The prestressing force produced between the two connecting rods holds the sockets against the balls. The prestressing also provides the required restoring moment that prevents the rods from twisting due to friction, dynamic forces, and forces exerted by components mounted on the rods such as vacuum hoses. In lieu of rubber-elastic O-rings, U.S. Pat. No. 6,419,211 has disclosed non-paired spring elements that have two angled elements with compression springs situated between them.
In the event of an overload, i.e. when the loads on the joints become greater than the prestressing forces, the joints decouple, which is a desired safety function and prevents the destruction of the robot.
It is disadvantageous that this decoupling is not detected. Consequently, even when one parallelogram rod assembly has already decoupled, the actuating arms of the delta robot continue to move, which leads to uncontrolled movements of the robot. The remaining connecting rod pairs or the support element can be hurled outward in an uncontrolled fashion and may possibly be damaged. Since the system itself does not discover that the robot is no longer functional, the system continues to run without taking suitable steps, e.g. stopping the entire system or having production taken over by the remaining robots.
It is therefore desirable for a decoupling of a joint to be immediately detected.
In a design known from US 2005/0177279, an acceleration sensor mounted on the support element detects a tilting of the support element caused by the decoupling of the connecting rods. This design is comparatively expensive and requires a set of electronics on the support element, thus increasing its weight. The required cables and the cable breakage due to the high cycle number of the delta robot of 200 cycles/minute represent an additional problem in terms of service life. The cables can be damaged when the decoupling occurs and also prevent the robot from being disassembled.
There have already been attempts to use the dynamic properties of the robot or the drive moments and power consumption of the motors as a basis for drawing conclusions about the completeness of the robot structure. But since these parameters are also changed by the load of the robot at the gripper, it is not easy to implement such designs.
U.S. Pat. No. 6,516,681 has disclosed a robot with parallel kinematics that has four parallelogram rod assemblies.